SQL_CALC_FOUND_ROWS / FOUND_ROWS() does not work in PHP

Question

I use SQL_CALC_FOUND_ROWS in Mysql SELECT statement, to get the number of lines my SELECT would return without a LIMIT clause.

$sql = new mysqli         


        

Answer 1

Well, it was a problem with mysql php extension bundled with php 5.2.6. Mysqli run fine, and another php version too. Sorry for noise and unclear question.

If you have the same problem, my advice is to re-install PHP or change version.

Answer 2

Thank you.

When I ran something analogous to your example on the mysql command line, it would work; but running it from php, it failed. The second query has to "know about" the first one, so I figure somehow that persistence/memory linking the two queries was getting messed up by the php.

(It turns out that Wordpress uses this type of query to do its pagination - so our larger problem was that the pagination in a wordpress install suddenly stopped working when we moved to php 5.2.6 ... eventually tracked it down to the FOUND_ROWS()).

Just for the sake of posting for people who may run into this in the future... for me it was the php setting "mysql.trace_mode" - this defaulted "on" in 5.2.6 instead of "off" like previously, and for some reason prevents the FOUND_ROWS() from working.

As a "fix", we could either put this in every php page (actually, in a common "include"):

ini_set("mysql.trace_mode", "0");

or add this to the .htaccess:

php_value mysql.trace_mode "0"

Thanks again, Jerry

Answer 3

Another way would be to use mysqli_multi_query as stated in the PHP manual by passing both queries containing SQL_CALC_FOUND_ROWS and FOUND_ROWS separated with a semicolon

<?php
$mysqli = new mysqli("localhost", "my_user", "my_password", "world");

/* check connection */
if (mysqli_connect_errno()) {
    printf("Connect failed: %s\n", mysqli_connect_error());
    exit();
}

$query  = "SELECT SQL_CALC_FOUND_ROWS * FROM db limit 0, 3;";
$query .= "SELECT FOUND_ROWS()";

/* execute multi query */
if ($mysqli->multi_query($query)) {
    do {
        /* store first result set */
        if ($result = $mysqli->store_result()) {
            while ($row = $result->fetch_row()) {
                printf("%s\n", $row[0]);
            }
            $result->free();
        }
        /* print divider */
        if ($mysqli->more_results()) {
            printf("-----------------\n");
        }
    } while ($mysqli->next_result());
}

/* close connection */
$mysqli->close();
?>

Answer 4

The quickest solution is to subquery your actual query like this:

SELECT SQL_CALC_FOUND_ROWS * FROM (SELECT whatever FROM whatever WHERE whatever LIMIT whatever) ax; 
select FOUND_ROWS();

Now you will get the correct results. I think the main reason being that SQL_CALC_FOUND_ROWS mainly tracks rows found (i.e. without LIMITS) not rows returned.

Answer 5

Are you using a MySQL query method that allows for multiple queries.

From MySQL documentation.

To obtain this row count, include a SQL_CALC_FOUND_ROWS option in the SELECT statement, and then invoke FOUND_ROWS() afterward

Example:

mysql> SELECT SQL_CALC_FOUND_ROWS * FROM tbl_name
    -> WHERE id > 100 LIMIT 10;
mysql> SELECT FOUND_ROWS();

Also just for fun, there's a great discussion about the race condition of FOUND_ROWS()'s usage here.

Answer 6

I had the same issue. The solution was stupid, I was using $wpdb->query instead of $wpdb->get_var. So you want to do

$wpdb->get_var('select FOUND_ROWS()');

if you're on WordPress